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Topic: GSLV MK III Core Stage (Read 7437 times)

GSLV MK III is very similar to the Ariane 5. Both have solid boosters. As everyone knows the weak link for the GSLV MK III is the core stage. Ariane has a great core with the EPC H158 stage. ISRO is planning to change the core stage of GSLV MK III from L110 to a Semi-Cryogenic stage when the SCE200 engine is ready that will increase the GSLV capability to launch 6 ton satellites to GTO.

Could ISRO have done better if they had worked on a core stage based on a more powerful Cryogenic engine instead - like a C170 LOX/LH2 stage with specs like a thrust of 1200kN and Specific Impulse of around 430-440 on a propellant load of around 170 tons? Currently what differentiates the ESA's Arianne 5 (that has 10.5 tons to GTO capability) from GSLV MK III is their core EPC H158 stage based on LOX/LH2 with a specific impulse of 440. Core stages need to have a high Specific Impulse to get the extra delta-v. So a Cryogenic core (with a high Specific Impulse) is a must for a heavy launcher to get the extra delta-v. With a Cryogenic core as above, GSLV MK III would have been a launcher in the 10 ton to GTO class.

Did ISRO miss an easy opportunity to get to the 10-ton class? Why did they prioritise the Semi-Cryo engine instead that gives then hardly an addition of 2 tons more than the current GSLV MK III?

If long term plan is to stay with Ariane 5 type configuration then large LOX/LH2 engine makes sense. A RP1 engine allows them to make multi engine boosters that don't need large SRBs, something like Atlas or F9. With 5 engine a RLV like F9 becomes an option.

Cost? Perhaps they realize that chasing the efficiency curve with huge cryo engines is very costly, and that semi-cryo will be more cost efficient and also a potential investment with future growth potential. (The industry trend seems to indicate a move towards reusable semi-cryo systems)

Also, the reason a high isp core stage would be so effective for the mk III is to make up for the poor efficiency (relatively speaking) of solid boosters.

IMO the solid boosters are the real anchor that holds mk III performance down, not the core stage. But it would of course be very costly develop a replacement for them too.

GSLV MK III is very similar to the Ariane 5. Both have solid boosters. As everyone knows the weak link for the GSLV MK III is the core stage. Ariane has a great core with the EPC H158 stage. ISRO is planning to change the core stage of GSLV MK III from L110 to a Semi-Cryogenic stage when the SCE200 engine is ready that will increase the GSLV capability to launch 6 ton satellites to GTO.

Could ISRO have done better if they had worked on a core stage based on a more powerful Cryogenic engine instead - like a C170 LOX/LH2 stage with specs like a thrust of 1200kN and Specific Impulse of around 430-440 on a propellant load of around 170 tons? Currently what differentiates the ESA's Arianne 5 (that has 10.5 tons to GTO capability) from GSLV MK III is their core EPC H158 stage based on LOX/LH2 with a specific impulse of 440. Core stages need to have a high Specific Impulse to get the extra delta-v. So a Cryogenic core (with a high Specific Impulse) is a must for a heavy launcher to get the extra delta-v. With a Cryogenic core as above, GSLV MK III would have been a launcher in the 10 ton to GTO class.

Did ISRO miss an easy opportunity to get to the 10-ton class? Why did they prioritise the Semi-Cryo engine instead that gives then hardly an addition of 2 tons more than the current GSLV MK III?

You seem to have hit the nail on the head. In one of my earlier posts I stated very much similar to what you have stated here. GSLV MK-III's core stage L-110 seems to be the week point for the whole vehicle, thus reducing its payload capability substantially. Had the core stage been propelled by cryogenic engines with a thrust of 1000 to 1200 kN and had it been longer than its current stage, GSLV MK-III would have matched nearly the same payload capability that the Ariane 5.

But the problem is that when ISRO designed GSLV MK-III in early 2000, it was still struggling with the development of CE-7.5 Cryogenic Engine that has delayed the CE-20 Cryogenic Engine. With a two stage rocket, with the first stage being propelled by Hypergolic and with shorter duration of burn, you can't expect a launch vehicle to launch a higher payload with the Cryogenic engine propelled upper stage. It is the core stage with higher ISP provided by cryogenic engine and burning for a longer period takes the bulk of weight off the ground and enables the Launcher to launch higher payload. But in the case of GSLV MK-III it is the Cryogenic Upper stage that need to exert more pressure to not only to inject the satellite into the GTO but also to do some extra work left over by the weaker core stage L-100 that is air-lit.

Now as ISRO has successfully mastered the High Thrust Cryogenic Engine indigenously, it is now time for ISRO not to give up further development of higher thrust cryogenic engine not only for Upper stage but also for core Stage. After the stupendous success of the CE-20 Cryogenic Engine and C25 Cryogenic stage, it is incumbent upon ISRO not to fritter away the technological gain it has achieved in the last twenty years against the backdrop of persistent technology denial by the technology denial regime such as MTCR by NOT embarking upon a project to develop a Core Stage with Cryogenic Propulsion either by developing a more powerful cryogenic engine ( 500 - 600 kN thrust ) to cluster 2 engines just as the Chinese did or clustering 5 CE-20 Cryogenic engine of 200 kN

Ultimately it is the Cryogenic Rocket Propulsion that would win space race as evidently noticed by the fact that the erstwhile Soviet Space program vis-a-vis the Manned Moon Mission foundered because of its failure to build powerful cryogenic engine. It is not until 1987 that Soviet Union developed a powerful cryogenic engine for its Energia Rocket and Buran space plane just barely 3 years before its unfortunate dismemberment. By the time around ( in 1987 ) Soviet Union developed a very powerful cryogenic rocket engine RD-0120( The 3rd powerful cryogenic engine with thrust of 1961 kN ) after RS-68 ( 3370 kN ) and Space Shuttle Main Engine ( 2278 kN ), the space race appeared to have been lost for them. Since then the Soviet Union [ current Russia ] failed to match with the powerful Rockets developed and operationalized by the USA, Europe, even Japan and finally China. All of these space fairing nations have very powerful cryogenic engines used in the core stages of their LV. Even though Chinese Cryogenic engines are not as powerful as those of other mentioned space power, they have clustered 2 YF-77 Cryogenic Engine ( 700 kN thrust ) to develop the core stage CZ-5-500 for their newly unveiled Long March 5, a launch vehicle that is comparable to and second to none than US Delta IV Heavy in terms of the launch capability performance amongst the current Launch Vehicles.

If ISRO can develop a core stage with 5 meter diameter clustered with 5 CE-20 Engine that can generate 1000 kN thrust, GSLV MK-III's payload capability would be significantly raised to almost 10 ton. It would be unwise of ISRO to renege the development of more powerful cryogenic engine to give way for the development semi-cryogenic engine. Semi-Cryogenic Engines would be temporary solution, but more powerful cryogenic engine should be permanent solution.

If ISRO can develop a core stage with 5 meter diameter clustered with 5 CE-20 Engine that can generate 1000 kN thrust, GSLV MK-III's payload capability would be significantly raised to almost 10 ton. It would be unwise of ISRO to renege the development of more powerful cryogenic engine to give way for the development semi-cryogenic engine. Semi-Cryogenic Engines would be temporary solution, but more powerful cryogenic engine should be permanent solution.

If you had written this 10 or 20 years ago, I would perhaps have agreed. But large hydrolox cryo booster stages have turned out to not be the magic bullet that people hoped for. Costs are high, in some cases very high.

So why follow competitors down that dead end when you can instead aim for where they are going?

A decent Cryo core (> 1200kN) with 2 good boosters (either solid or RP-1/LOX) each with around 5000kN thrust. This is similar to the Ariane.

But if you have a Semi-Cryo core then it better be big like the Falcon 9's. Semi-Cryo cores stages of 4000kN thrust even with boosters of around the same thrust simply do not hack more than 4 ton payload because what is needed for the core stage is delta-v and Semi-cryo engines with spec imp of around 330s simply don't provide it. Falcon 9's core stage of clustered 9 Merlin 1D engines is unbelievably amazing technology that would be hard to beat by other organisations. A single 1D engine generates only 934kN thrust on a propellant load of 107.5 tons. But when they cluster 9 of them then can generate thrust of 8227kN (near linear progression) on a propellant load of 410 tons (less than half of linear progression). This is amazing. This cannot simply be matched by any other.

This is what i could figure out with some simple delta-v calculations. A good Cryogenic core stage instead of a kerosine core would certainly have increased the payload of the GSLV MK III to around 10.

On a similar note, another discussion point is the following:If increasing the payload of GSLV is the main challenge then why cant an additional higher stage be added in the form of a CUS12 stage with the CE7.5 engine on top of the current C25 stage that would give it an additional delta-v? That would help to increase the payload from 4 tons to around 7 tons (if delta-v are worked out for each stage, looks reasonable) class, without any new development. Dont know why ISRO is not going this route? The CUS12 stage is 2.8m diameter while the the C25 stage is 4M diameter. So they may need to do some air flow tests probably.

I'm with Lars-J. Cryogenic cores with solid boosters are an expensive way to get to orbit. Look at what SpaceX and Blue Origin are doing. These are commercial companies that actually seek to reduce cost. My recommendation is that ISRO cluster seven of the SCE-200 at 2 MN each to have a booster with 14 MN of thrust. With a cryogenic upper stage, that should give great performance as well as allowing the booster to be reused.

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Akin's Laws of Spacecraft Design #1: Engineering is done with numbers. Analysis without numbers is only an opinion.

I have read that the low density of LH2 necessitate the usage of larger propellant tanks which would somewhat negate the advantages of its use as a core stage (as against a smaller upper stage). But then we do have old and new rocket designs that use a hydrolox core (with Long March 5 being the latest entrant), so I guess the higher Isp sufficiently compensates for that. That would leave us the question of cost.

Secondly, ISRO has (or had) plans to use the SCE-200 powered kerolox core with a combination of smaller solids to create simpler launch vehicles (considering the number of stages and propulsion units) that would replace PSLV and GSLV-II. So they were evidently planning to use a common core across a whole family of launch vehicles ( a.k.a ULV ), and not just the high-end. So going for a kerolox core may have appeared as a more flexible option. But I do not know if they are still sticking to those plans. Unlike their stated objective to cluster SCE-200 to create larger SC400 or SC500 cores, their recent presentations doesn't seem to have addressed the question of what they plan to do with the lower end of the payload spectrum that is covered currently by PSLV and GSLV-II.

1x Sce200 core with existing SRBs is good short term goal, it allows them compete for most GTO missions and gives new engine flight tiime. A RLV is definitely one of ISRO long term goals, here they have couple options using SCE200. 1 xSCE200 VTHL flyback booster for PSLV market, this is something they should be able to do and PSLV has market to make it worthwhile. Follow this with large multi engine VTOL booster in F9 class.

I have read that the low density of LH2 necessitate the usage of larger propellant tanks which would somewhat negate the advantages of its use as a core stage (as against a smaller upper stage). But then we do have old and new rocket designs that use a hydrolox core (with Long March 5 being the latest entrant), so I guess the higher Isp sufficiently compensates for that. That would leave us the question of cost.

But the Long March 5 was not started today. It was started years ago as a response to the Delta IV. (which ULA wants to retire as soon as possible due to absurdly high costs)

If you only try to build what competitors are flying *now*, you'll always be 5-10 years behind the curve. See where others are going, and aim for that. Then you might actually be able to surpass them.

I have read that the low density of LH2 necessitate the usage of larger propellant tanks which would somewhat negate the advantages of its use as a core stage (as against a smaller upper stage). But then we do have old and new rocket designs that use a hydrolox core (with Long March 5 being the latest entrant), so I guess the higher Isp sufficiently compensates for that. That would leave us the question of cost.

But the Long March 5 was not started today. It was started years ago as a response to the Delta IV. (which ULA wants to retire as soon as possible due to absurdly high costs)

If you only try to build what competitors are flying *now*, you'll always be 5-10 years behind the curve. See where others are going, and aim for that. Then you might actually be able to surpass them.

"There are some who question the relevance of space activities in a developing nation. To us, there is no ambiguity of purpose. We do not have the fantasy of competing with the economically advanced nations in the exploration of the moon or the planets or manned space-flight. But we are convinced that if we are to play a meaningful role nationally, and in the community of nations, we must be second to none in the application of advanced technologies to the real problems of man and society." --- By the GREAT himself

I have read that the low density of LH2 necessitate the usage of larger propellant tanks which would somewhat negate the advantages of its use as a core stage (as against a smaller upper stage). But then we do have old and new rocket designs that use a hydrolox core (with Long March 5 being the latest entrant), so I guess the higher Isp sufficiently compensates for that. That would leave us the question of cost.

But the Long March 5 was not started today. It was started years ago as a response to the Delta IV. (which ULA wants to retire as soon as possible due to absurdly high costs)

If you only try to build what competitors are flying *now*, you'll always be 5-10 years behind the curve. See where others are going, and aim for that. Then you might actually be able to surpass them.

"There are some who question the relevance of space activities in a developing nation. To us, there is no ambiguity of purpose. We do not have the fantasy of competing with the economically advanced nations in the exploration of the moon or the planets or manned space-flight. But we are convinced that if we are to play a meaningful role nationally, and in the community of nations, we must be second to none in the application of advanced technologies to the real problems of man and society." --- By the GREAT himself

So why pursue near useless hydrolox booster stages? Is it just a status symbol, to say that India has technology X? Then what real use to man and society is it? Do you "play a meaningful role nationally, and in the community of nations" by repeating the same mistakes of other nations?

I have read that the low density of LH2 necessitate the usage of larger propellant tanks which would somewhat negate the advantages of its use as a core stage (as against a smaller upper stage). But then we do have old and new rocket designs that use a hydrolox core (with Long March 5 being the latest entrant), so I guess the higher Isp sufficiently compensates for that. That would leave us the question of cost.

But the Long March 5 was not started today. It was started years ago as a response to the Delta IV. (which ULA wants to retire as soon as possible due to absurdly high costs)

If you only try to build what competitors are flying *now*, you'll always be 5-10 years behind the curve. See where others are going, and aim for that. Then you might actually be able to surpass them.

"There are some who question the relevance of space activities in a developing nation. To us, there is no ambiguity of purpose. We do not have the fantasy of competing with the economically advanced nations in the exploration of the moon or the planets or manned space-flight. But we are convinced that if we are to play a meaningful role nationally, and in the community of nations, we must be second to none in the application of advanced technologies to the real problems of man and society." --- By the GREAT himself

So why pursue near useless hydrolox booster stages? Is it just a status symbol, to say that India has technology X? Then what real use to man and society is it? Do you "play a meaningful role nationally, and in the community of nations" by repeating the same mistakes of other nations?

I'm not exactly sure what @kanaka was trying to say with the quote posted above. Perhaps he was trying to describe what ISRO's original mandate was, and how that shaped its approach to launch vehicle tech. It was the words of the late Vikram Sarabhai at the inception of ISRO (or maybe its predecessor INCOSPAR) many decades back. For sure, ISRO has moved beyond the 'bread and butter' aspects of its mandate and has forayed into lunar and interplanetary exploration now. Now ISRO's vision document in its website says - "Our vision is to harness space technology for national development, while pursuing space science research and planetary exploration." So I would expect a more confident ISRO to start dipping its toes in unexplored and uncharted waters in the coming years, and move beyond copying what others have already done before, gradually of course.

That said I do not think ISRO has any plans at the moment to build big hydrolox cores for its future rockets. Their recent presentations all pointed to to plans to cluster SCE-200 kerolox engines into an SC400 or SC500 core, with ~400 T and 500T propellant loadings respectively. Hydrolox stages in their plans are meant to be upper stages.

On a similar note, another discussion point is the following:If increasing the payload of GSLV is the main challenge then why can't an additional higher stage be added in the form of a CUS12 stage with the CE7.5 engine on top of the current C25 stage that would give it an additional delta-v? That would help to increase the payload from 4 tons to around 7 tons (if delta-v are worked out for each stage, looks reasonable) class, without any new development. Dont know why ISRO is not going this route? The CUS12 stage is 2.8m diameter while the the C25 stage is 4M diameter. So they may need to do some air flow tests probably.

Understand your points from a long term point of view. In the short term, for a quick increase of payload, any idea why ISRO should not do the above? Any restrictions, thoughts, comments?

Wouldn't adding CUS7.5 over CE12 reduce the payload capacity ? to the extent of the weight of CUS7.5 stage ?

That's how staging can improve performance. CUS7.5 presumably is much smaller/lighter, which allows more delta-v to be squeezed out by dropping off the heavier CE12. But it doesn't always make sense. stretching the CE12 could produce more performance.

CUS12 stage (CE7.5 engine) not as a replacement for the C25 stage (CE20 engine).CUS12 stage in addition to the C25 as an additional stage.

So the vehicle will be a 4 stage rocket instead of 3 stage.

Now it has stage1-boosters, stage2-L110, stage3-C25Proposed is stage1-boosters, stage2-L110, stage3-C25, stage4-CUS12

The extra stage adds an extra 15.3 tons to the vehicle. So the extra weight will reduce the delta-v attained by each of the previous stages. But the additional stage will contribute the maximum final bump of delta-v.

1. GSLV-III's primary weakness is its underpowered L-110 core, and adding a fourth stage would be either detrimental or would not result in a meaningful upgrade in payload capabilities. Here is a relevant quote by S. Ramakrishnan (who was the project director of GSLV-III) from the book 'From fishing hamlet to red planet'.

Quote

The avenues for further enhancement of LVM-3 performance beyond 4 tonnes will definitely be explored once the vehicle stabilises after a few successful missions. Inert mass reduction in the upper stage (C25) and associated assemblies will be the most attractive and efficient route with least risk in terms of mission reliability. Of course, the propellant loading of C25 itself can be further augmented beyond 27 tonnes by stretching the tankages and also requalifying the endurance of the propulsion systems for the longer burn time. Modulating the engine thrust within bounds in terms of uprating/downrating during the long-stage burn time to optimise the needed velocity gain (ΔV), as was done with GSLV CUS stage, can be another strategy to marginally stretch the performance. However, without touching the lower propulsive stages and the overall vehicle architecture the payload growth of GSLV-Mk III may not go beyond 5 tonnes to GTO. With the ongoing programme to develop a 200 tonne thrust LOX-Kerosene semi-cryo engine and subsequently a semi-cryo stage to replace the L110 core, the GTO payload is expected to touch 6 tonnes.

2. The ongoing project to upgrade core stage to SC-200 is a better option in terms of simplicity and reliability than adding another upper stage. Adding a 4th stage would make the vehicle more complex and adds another point of potential failure.

3. GSLV-II's CUS (C-12/C-15) is too heavy for the job as an added 4th stage. A new smaller stage would be required.

4. The much lower diameter of CUS (~2.8m) would introduce complications in the flight characteristics of the vehicle during its atmospheric phase of ascent. This necessitates extensive retesting of the stack in wind tunnels and the rocket would most likely require a host of other hardware and control software modifications to accomodate the change.

5. CUS's CE-7.5 (~75-98 kN) being nearly half as powerful as CE-20 (~180-200 kN) of the preceding C-25 third stage is over-powered for the desired flight profile. A smaller cryo engine needs to be developed.

6. The 5.7 tonne GSAT-11 is a one-off for the time being, and ISRO is betting heavily on electric propulsion to keep the weight of its comsats to a 4-5 tonne level. Developing new all-electric satellite buses of 3 or 4 tonne class would allow ISRO to pack as much transponders as the 5 and 6 tonne satellites equipped with conventional propulsion do, and get it launched at cheaper costs using existing GSLV-III.

7. ISRO does not expect GSLV-III to make a big entry into international commercial launch business any time soon due to current production constraints. Their plan for the near term to increase combined launch count to 12 per year envision only one GSLV-III and two GSLV-II (the rest 9 being PSLVs). They would most likely need them for domestic payloads. So there isn't much sense in attempting ad-hoc measures to increase the payload of GSLV-III for the sake of foreign satellite launch business either. For the small numbers of GSLV-III that happen to become available for commercial flights in the immediate future, they could look for sub-4 tonne conventional or all-electric satellites.

To add to my previous post, there could be a potential external constraint for PonRam's config for a GSLV-III with an added CUS as the 4th stage, assuming it is a feasible design in every other way.

In the current flight profile of GSLV-III, the L-110's burn duration has been adjusted so that it separates and falls into the Andaman sea right before it encounters Malay peninsula and the Indonesian islands. (See here) C-25 of course enters orbit together with its payload.

For the new configuration (assuming other constraints are surmountable), I guess it would be fair to expect that L-110 would separate a bit before as it carries a heavier load. This should be acceptable as the flight path till then is mostly over open sea.

But the question in my mind is about C-25. Carrying a heavier satellite and an added CUS 4th stage, it is quite likely that the stage would be on a suborbital flight when CUS and the satellite stack separates. Where then would it's debris fall? If my understanding of the flight path is correct, after the Andaman sea the flight passes over a long region of Indonesian islands and territorial waters. C-25 falling anywhere there would be darn risky and unacceptable.